1. FIELD OF THE INVENTION
The present invention relates to a bridge plug employing an inflatable elastomeric packing element to permit the bridge plug to be passed into a subterranean well bore through relatively small diameter production tubing. During run-in and setting of the bridge plug, a tubular mandrel carried by the running tool engages a pressure balanced, axially shiftable valve plug to maintain the valve plug in an open position for fluid to flow downwardly into the inflatable elastomeric element. After inflation, the running tool is disengaged from the bridge plug and such disengagement effects a closing of the axially shiftable plug valve.
2. DESCRIPTION OF THE PRIOR ART
Those skilled in the art relating to remedial operations associated with drilling, production and completion of subterranean oil and gas wells have long utilized threaded or coupled remedial tubing inserted through production tubing, for pumping pressured fluid from the surface to a bridge plug having an inflatable elastomeric packing element. More recently, continuous coiled remedial tubing has frequently replaced threaded or coupled tubing to pass fluid to the inflatable elastomeric element, since coiled tubing may be more rapidly inserted into the well and may be easily passed through production tubing and related downhole equipment because its diameter is consistently the same size.
Typical remedial coiled tubing apparatus is described in the 1973 Composite Catalogue of Oil Field Equipment and Services, at page 662, and manufactured by Bowen Tools, Inc. of Houston, Tex. Apparatus related to this coiled tubing technique is more particularly described in U.S. Pat. Nos. 3,182,877 and 3,614,019. More recent advances, such as those disclosed in U.S. Pat. No. #4,349,204, enable the inflatable bridge plug to pass through a small diameter production tubing, effect seal with a larger diameter casing, and then be retrievable to the surface through the small diameter tubing.
When it is desired to insert an inflatable bridge plug into a subterranean well by passage through a relatively small diameter production tubing, a problem arises in maintaining circulation between the tubing bore and the annulus during run-in. This necessarily requires that a valve plug of some type be incorporated in the bore of the bridge plug to permit fluid passage therethrough during run-in, but then being shiftable to a closed position after the setting of the inflatable bridge plug is accomplished. This creates a new problem in that the valve plug is subjected to the pressure of the well fluids surrounding the bridge plug and hence is very difficult to re-open for retrieval unless such pressure is substantially equalized.
A further problem arises when coiled tubing is utilized to run-in the inflatable bridge plug. As is well known, the amount of compressive force exertable by coiled tubing is very limited, due to its tendency to buckle. It is therefore essential that the valve plug be shiftable to an open position by a setdown weight which does not require any significant compression of the coiled tubing.